Anticorrosive rare earth alloy composite material, preparation method and application thereof

Abstract

The application discloses a corrosion-resistant rare earth alloy composite material and a preparation method and application thereof. The corrosion-resistant rare earth alloy composite material comprises, from inside to outside or from bottom to top, a carbon steel base and a coating layer, wherein the coating layer comprises a rare earth alloy layer and a corrosion-resistant hole sealing layer; the surface of the carbon steel base is etched with main pits at a spacing of 10-20 microns, the diameter of the main pit is 40-60 microns, and the depth is 15-25 microns; the rare earth alloy layer is an Al-Zn-Ce-Mg-Sc alloy powder, and the surface of the rare earth alloy layer is a nitrided layer containing CeN and AlN; the corrosion-resistant hole sealing layer comprises siloxane 40-60%, epoxy resin 25-35%, shape memory polyurethane 10-20%, nano-montmorillonite 3-8%, dibutyltin dilaurate 0.3-0.8%, and a sol formed by stirring. The application solves the problems of the existing corrosion-resistant materials, such as insufficient bonding force, low density, poor corrosion resistance, short service life and poor high-temperature adaptability.

Description

Technical Field

[0001] This invention relates to the field of anti-corrosion materials technology, and in particular to anti-corrosion rare earth alloy composite materials, their preparation methods and applications. Background Technology

[0002] Air preheaters are key equipment in boiler systems for recovering waste heat from flue gas and improving energy efficiency. Their core components are mostly made of metal materials such as carbon steel. However, air preheaters operate for extended periods under high temperatures (200-400℃), high humidity (flue gas moisture content 10%-20%), and highly corrosive media (containing SO2, NO). x In complex operating conditions involving acidic gases such as HCl and fly ash particles, metal components are prone to severe corrosion and wear, leading to a shortened equipment lifespan (the average lifespan of a traditional air preheater is only 3-5 years), a decrease in heat exchange efficiency (reduced by 5%-8% annually), and even safety hazards such as flue gas leaks, resulting in high maintenance costs.

[0003] Existing air preheater corrosion protection technologies have the following limitations:

[0004] Insufficient coating adhesion: Traditional anti-corrosion coatings (such as enamel and ordinary rare earth alloy coatings) are mostly physically attached to carbon steel substrates. Under the action of high-temperature alternating stress (the temperature difference reaches more than 200°C when the air preheater starts and stops), they are prone to peeling off, and local corrosion will appear in 3-6 months.

[0005] Sacrificial anode activity is unstable: the electrode potential of conventional rare earth alloy coatings fluctuates greatly (±0.05V), which cannot continuously and efficiently protect the substrate. It loses its protective ability due to activity decay within 1-2 years.

[0006] The protective layer has weak resistance to damage: fly ash particles in the flue gas (with a hardness of up to 500HV) severely erode and wear the coating. Traditional sealing agents (such as epoxy resin) have no self-healing function, and once cracks appear, they will cause corrosive media to penetrate.

[0007] Poor high-temperature adaptability: Most organic anti-corrosion materials will undergo thermal aging (such as degradation and embrittlement) above 200℃, resulting in a sharp drop in protective performance and making them unable to adapt to the long-term high-temperature operating environment of air preheaters.

[0008] To address the aforementioned issues, while existing technologies have attempted to improve corrosion resistance by modifying coating formulations (such as adding nanoparticles) or optimizing spraying processes (such as supersonic flame spraying), they have failed to fundamentally solve the synergistic problem of "bonding strength, activity stability, damage resistance, and high-temperature adaptability." Therefore, developing a method for preparing rare-earth alloy composite materials suitable for air preheater operation, possessing high bonding strength, long-lasting sacrificial anode activity, intelligent self-healing capabilities, and high-temperature corrosion resistance, has become a pressing technical challenge in this field. Summary of the Invention

[0009] To address the problems of insufficient bonding strength, low density, poor corrosion resistance, short service life, and poor high-temperature adaptability of existing anti-corrosion materials, this invention provides an anti-corrosion rare earth alloy composite material, which, from the inside out or from the bottom up, sequentially includes a carbon steel substrate and a coating, wherein the coating includes a rare earth alloy layer and a corrosion-resistant sealing layer.

[0010] The carbon steel substrate surface is etched with main pits at intervals of 10-20 μm, the main pits having a diameter of 40-60 μm and a depth of 15-25 μm.

[0011] The rare earth alloy layer is an Al-Zn-Ce-Mg-Sc alloy powder, and the surface of the rare earth alloy layer is a nitride layer containing CeN and AlN.

[0012] The corrosion-resistant sealing layer includes:

[0013] A sol is formed by stirring 40-60% siloxane, 25-35% epoxy resin, 10-20% shape memory polyurethane, 3-8% nano-montmorillonite, and 0.3-0.8% dibutyltin dilaurate.

[0014] Preferably, the bottom of the main pit in the carbon steel substrate is etched with secondary pits with a diameter of 1-2 μm and a depth of 0.5-1 μm at intervals of 1-3 μm.

[0015] Preferably, the surface of the main and secondary pits of the carbon steel has 50-100nm nanofibers.

[0016] Preferably, the mass ratio of the rare earth alloy layer Al-Zn-Ce-Mg-Sc alloy powder is (45-55):(25-35):(8-12):(5-10):(1-3), and the particle size is 20-40μm.

[0017] Preferably, the coating further includes a polydopamine-carbon nanotube hybrid layer and a CaSiO3-HAP composite mineralization layer;

[0018] Preferably, the polydopamine-carbon nanotube hybrid layer is disposed between the corrosion-resistant sealing layer and the rare earth alloy layer, and the CaSiO3-HAP composite mineralization layer is disposed between the polydopamine-carbon nanotube hybrid layer and the corrosion-resistant sealing layer.

[0019] In addition, the present invention also provides a method for preparing the above-mentioned corrosion-resistant rare earth alloy composite material, comprising the following steps:

[0020] S100: Pretreatment of carbon steel matrix

[0021] S110: After ultrasonic rust removal and cleaning of the carbon steel substrate in dilute hydrochloric acid, laser etching is used to etch the spacing between the main and secondary pits on the carbon steel substrate. Then, a second scanning process is used to form nanofibers on the surface of all pits.

[0022] S120: The carbon steel substrate treated with S110 is immersed in an ethanol-water mixed solution containing La2O3 quantum dots. After ultrasonic treatment, the quantum dots are electrostatically adsorbed onto the Fe on the carbon steel surface. 2+ La-Fe coordination bonds are formed;

[0023] S200: Deposition and densification of rare earth alloy layers

[0024] S210: Place Al-Zn-Ce-Mg-Sc alloy powder in supercritical CO2 fluid, add CeCl3 as an activator, stir for 1-1.5h to form activated powder with CeO2 nano-active layer on the powder surface;

[0025] S220: After the carbon steel matrix treated with S210 is preheated in a gradient, supercritical He is used as the carrier gas to spray the activated powder onto the carbon steel matrix. At the same time, a DC electric field is applied to promote the transfer of surface charge of powder particles through electric field force and accelerate ion diffusion.

[0026] S230: The deposited rare earth alloy layer is placed in a strong magnetic field, and a high-energy electrical pulse is applied to scan along the coating thickness direction.

[0027] S240: In a vacuum reaction chamber, N2-Ar mixed gas is introduced to apply radio frequency plasma, and nitriding is performed at 200°C for 1.5-2 hours to form a nitrided layer containing CeN and AlN on the coating surface.

[0028] S300: Forming of corrosion-resistant sealing layer

[0029] S310: Siloxane, epoxy resin, shape memory polyurethane, nano-montmorillonite, mixed and then dibutyltin dilaurate catalyst is added and stirred to form a sol.

[0030] S320: Vacuum dip coating is used to penetrate the sol into the rare earth alloy layer, ensuring a penetration depth of 3-7μm. After removal, it is allowed to level in the air for 0.5-1h.

[0031] S330: First, treat in a vacuum oven at 30-50℃ for 1-1.5h to remove the solvent, then raise the temperature to 70-90℃ and hold for 1.5-2h to promote the cross-linking of siloxanes, and finally raise the temperature to 100-120℃ and hold for 1-1.5h to completely cure the shape memory polyurethane and epoxy resin.

[0032] Preferably, in step S220, the temperature of the carbon steel substrate gradient preheating center region is 300-400℃, and the temperature of the edge region is 200-300℃.

[0033] Preferably, before the sol-gel infiltration into the rare earth alloy layer in step S320, the method further includes:

[0034] S250: Spray a mixture of dopamine solution and carbon nanotubes onto the rare earth alloy layer after step S240 to form a polydopamine-carbon nanotube hybrid layer.

[0035] S260: Immerse the rare earth alloy layer treated in step S250 into a Ca-containing solution. 2+ With SiO3 2- In simulated body fluid, mineralization at 37℃ for 36-48 hours resulted in the formation of a CaSiO3-HAP composite mineralization layer.

[0036] Preferably, in step S250, the pH of the dopamine solution is 8-9, benzotriazole is added to the dopamine solution, and the amount of carbon nanotubes added is 0.07-0.12% of the dopamine solution;

[0037] In step S260, Ca 2+ The concentration of SiO3 is 0.05 mol / L. 2- The concentration was 0.03 mol / L.

[0038] The present invention provides the above-mentioned corrosion-resistant rare earth alloy composite material for use in tube bundles in air preheaters.

[0039] Compared with the prior art, the beneficial effects of the present invention are:

[0040] Significantly enhanced bonding strength: Through the pretreatment of the matrix with "quantum dot anchoring-multi-level texture", a three-level bonding interface of "molecule-micron-nano" is constructed, and the basic bonding strength is increased to 3 times that of the traditional process; under the synergistic effect of each link, the final bonding strength reaches 85MPa, far exceeding the approximately 40MPa of the traditional thermal spraying.

[0041] High coating density: Electric field-assisted supercritical cold spraying increases the coating density from 92% in traditional cold spraying to 99.5%, effectively reducing the impact of porosity on corrosion resistance.

[0042] Excellent corrosion resistance: sacrificial anode life extended to 8 years (traditional 5 years), no corrosion after 2500h salt spray test, far superior to the 1000h level of traditional sealing agents; corrosion rate reduced to 0.0005mm / a in acidic environment;

[0043] It features intelligent protection: it introduces a pH-responsive polydopamine-carbon nanotube hybrid layer to achieve a dual function of "corrosion warning-active repair"; the sealing agent has the ability to self-repair microcracks and can restore its original shape by heating;

[0044] Good process compatibility: The temperature of each step is lower than the phase transformation point of carbon steel (727℃), avoiding the deterioration of the matrix properties, making it suitable for industrial mass production, and reducing the total energy consumption by 35%.

[0045] The corrosion protection principle of the corrosion-resistant rare earth alloy composite material prepared by this invention is as follows:

[0046] Laser etching of pits increases the specific surface area of ​​the carbon steel substrate. The macroscopic mechanical interlocking of the main pits and the microscopic capillary adsorption of the secondary pits and nanofibers significantly enhance the adhesion of the rare earth alloy layer. Simultaneously, the extremely low heat input of the laser ensures that the substrate performance is not compromised. La2O3 quantum dots adhere to the Fe on the steel surface through electrostatic adsorption. 2+ This combination forms La-Fe coordination bonds, providing atomic-level bonding sites for subsequent rare-earth alloy layers. Simultaneously, the pre-introduction of La lowers the elemental diffusion barrier between the subsequent rare-earth alloy layers and the substrate, reducing interfacial stress. Quantum dots (nanoscale) possess high surface energy and can interact with active sites on metal surfaces (such as Fe) through electrostatic interactions. 2+ A strong bond is formed, and ultrasonic vibration promotes the penetration of quantum dots into the micropores of the steel surface, achieving "nanoscale anchoring".

[0047] Supercritical CO2 combines the diffusivity of a gas with the solubility of a liquid, allowing CeCl3 to uniformly penetrate into the micropores of the powder surface. Under the high permeability of supercritical CO2, CeCl3 uniformly coats the surface of Al-Zn-Ce-Mg-Sc alloy powder and forms a CeO2 nanolayer, removing the oxide film on the powder surface and improving deposition activity. The CeO2 active layer easily reacts with the Fe matrix during subsequent deposition, promoting metallurgical bonding. Rare earth element Sc can refine the alloy grains and stabilize the electrode potential at -0.90±0.01V (compared to ±0.05V fluctuation in traditional formulations), ensuring the long-term effectiveness of the sacrificial anode activity.

[0048] The gradient temperature field allows for more complete plastic deformation of particles in the core area, reduces stress concentration in the edge area, and avoids coating cracking. The electric field promotes surface charge transfer of powder particles (accelerates ion diffusion). Combined with the high kinetic energy of supercritical He, the density of the coating is improved. Laser-induced Al-Zn-Ce and Fe form (Al,Ce)Fe2 intermetallic compounds to eliminate interfacial porosity and improve bonding strength.

[0049] The Joule heating of the electric pulse causes localized heating at micropores and microcracks. Combined with the electroplastic effect, this promotes metal flow to close defects and reduces porosity. The strong magnetic field guides the rare earth phase (such as CeZn5) to align along the magnetic field direction, enhancing the electrochemical activity of the rare earth alloy layer and making the current distribution more uniform.

[0050] High-energy N in plasma + Ions bombard the coating surface under electric field acceleration, reacting with elements such as Ce and Al to form high-hardness nitrides; low temperature (200℃) avoids oxidation and burn-off of rare earth elements, retaining their electrochemical activity; the nitride layer significantly improves the hardness of the rare earth alloy layer, enhancing the coating's resistance to fly ash abrasion; CeN and AlN, as "sacrificial anode reserve phases", are slowly released with surface corrosion, extending the sacrificial anode life.

[0051] Dopamine self-polymerizes under weakly alkaline conditions to form polydopamine (PDA). The catechol and amine groups in its molecular structure can adhere to the surface of almost all materials through hydrogen bonding, π-π stacking, and other interactions. The conductive network formed by CNTs can accelerate the transmission of pH response signals, enabling the rapid release of the corrosion inhibitor benzotriazole. The catechol groups (-OH) of polydopamine form hydrogen bonds with the surface of rare earth alloys. Carbon nanotubes (CNTs) enhance the mechanical properties of the polydopamine-carbon nanotube hybrid layer and improve the bonding force. The amine groups (-NH2) of polydopamine are protonated (positively charged), releasing the benzotriazole pre-adsorbed by CNTs and inhibiting the corrosion reaction.

[0052] PDA's catechin groups can chelate Ca2+. 2+ Inducing SiO3 2- With Ca 2+ Co-deposition forms a CaSiO3-HAP composite mineralization layer (an organic-inorganic hybrid structure mimicking bone tissue), which combines the corrosion resistance of the inorganic phase with the flexibility of the organic phase. Needle-like CaSiO3-HAP crystals fill the micropores on the coating surface, further reducing the porosity. In the CaSiO3-HAP composite mineralization layer, the silicon-oxygen bonds (Si-O) undergo a condensation reaction with the siloxane in the corrosion-resistant sealing layer, further improving the bonding strength.

[0053] Shape memory polyurethane (SMPU) molecules contain soft segments (deformable at room temperature) and hard segments (forming physical cross-linking points). Upon heating, the movement of the soft segments closes the cracks. Siloxanes and epoxy resin form an interpenetrating network, combining the temperature resistance of the inorganic phase (stable above 200℃) with the flexibility of the organic phase. SMPU can recover its original shape above 60℃, repairing microcracks ≤50μm. Nano-montmorillonite layers are stacked layer by layer in the coating, extending the lifespan of corrosive media (Cl). - H + Diffusion path;

[0054] Vacuum conditions eliminate air bubbles during dip coating, allowing the sealing agent to fully penetrate nanoscale defects; gradient thermosetting causes the sealing agent to gradually cross-link from the surface to the deep layer, avoiding internal stress cracks caused by volume shrinkage and ensuring structural density; gradient heating can prevent the rapid evaporation of solvents from generating air bubbles, reducing internal stress; the vacuum environment promotes the penetration of the sealing agent into the micropores of the mineralized layer, forming a double isolation of "surface coverage + micropore filling" and improving corrosion resistance. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0056] Example 1

[0057] The corrosion-resistant rare earth alloy composite material, from the inside out or from the bottom up, includes a carbon steel matrix and a coating, the coating including a rare earth alloy layer and a corrosion-resistant sealing layer;

[0058] The surface of the carbon steel substrate is etched with main pits at 10μm intervals. The main pits have a diameter of 40μm and a depth of 15μm. Then, at the bottom of the main pits of the carbon steel substrate, secondary pits with a diameter of 1μm and a depth of 0.5μm are etched at 2μm intervals.

[0059] The rare earth alloy layer is an Al-Zn-Ce-Mg-Sc alloy powder with a mass ratio of 45:35:8:10:2 and a particle size of 20-40μm. The surface of the rare earth alloy layer is a nitrided layer containing CeN and AlN with a thickness of 5-10nm.

[0060] Corrosion-resistant sealing layer includes:

[0061] A sol was formed by stirring 40% siloxane (KH560), 35% epoxy resin (E51), 20% shape memory polyurethane (Tg=60℃), 4.7% nano-montmorillonite, and 0.3% dibutyltin dilaurate.

[0062] A method for preparing corrosion-resistant rare earth alloy composite materials includes the following steps:

[0063] S100: Pretreatment of carbon steel matrix

[0064] S110: After ultrasonic rust removal in 5% dilute hydrochloric acid and cleaning with deionized water, the carbon steel substrate is etched with a femtosecond laser (pulse width 100 fs, wavelength 800 nm) to create main pits on the surface. The main pits mimic a honeycomb structure. Sub-pits are then etched at the bottom of the main pits. Finally, a second scan is performed to form 50-100 nm nanofibers (mimicking gecko foot bristles) on the surface of all pits. The laser energy density gradient is adjusted (5 J / cm² in the main pit area). 2 3J / cm in the secondary pit area 2 1J / cm nanofiber region 2 ), to avoid excessive heat damage;

[0065] S120: The carbon steel substrate treated with S110 is immersed in an ethanol-water mixed solution (volume ratio 1:1) containing 0.1 mol / L La2O3 quantum dots (particle size 5-10 nm) and treated at 60℃ and ultrasonic power 300W for 2 hours, allowing the quantum dots to adhere to the Fe on the carbon steel surface through electrostatic adsorption. 2+ La-Fe coordination bonds are formed; La2O3 quantum dots act as "molecular rivets" to provide atomic-level bonding sites for subsequent rare earth alloy layers, while rare earth elements are introduced in advance to reduce the subsequent diffusion energy barrier;

[0066] S200: Deposition and densification of rare earth alloy layers

[0067] S210: Place Al-Zn-Ce-Mg-Sc alloy powder in supercritical CO2 fluid (temperature 31℃, pressure 7.3MPa), add 0.5% CeCl3 as activator, stir for 1-1.5h to form activated powder with CeO2 nano-active layer on the powder surface, the thickness of CeO2 nano-active layer is 5-10nm;

[0068] S220: After the carbon steel matrix treated with S210 is subjected to gradient preheating, the temperature of the central region of the gradient preheating is 300℃ and the edge region is 200℃. Supercritical He is used as the carrier gas (pressure 4MPa, temperature 150℃). The activation powder is sprayed onto the carbon steel matrix at a velocity of 800m / s, while a DC electric field (voltage 500V, current density 10mA / cm²) is applied. 2 The electric field promotes charge transfer on the surface of powder particles, thereby accelerating ion diffusion.

[0069] S230 places the deposited rare earth alloy layer in a 0.5T strong magnetic field and simultaneously applies a high-energy electrical pulse (voltage 1000V, pulse width 50μs, frequency 100Hz) and scans along the coating thickness direction for 5 minutes. The magnetic field causes the rare earth phase (such as CeZn5) in the coating to align in the direction of the magnetic field. The Joule heating and electroplastic effect of the electrical pulse causes the micropores and microcracks to close.

[0070] S240: Under a vacuum degree of 10 -3 In the reaction chamber of Pa, a N2-Ar mixed gas (volume ratio 1:3) is introduced, radio frequency plasma (power 300W) is applied, and nitriding is performed at 200℃ for 1.5-2h to form a 5-10μm nitrided layer containing CeN and AlN on the coating surface.

[0071] S300: Forming of corrosion-resistant sealing layer

[0072] S310: Siloxane, epoxy resin, shape memory polyurethane, nano-montmorillonite, mixed and then dibutyltin dilaurate catalyst is added and stirred to form a sol.

[0073] S320: Vacuum dip coating (vacuum degree -0.09MPa) is used to penetrate the sol into the micropores of the rare earth alloy layer, ensuring a penetration depth of 3-7μm. After removal, it is allowed to level in the air for 0.5-1h.

[0074] S330: First, treat in a vacuum oven at 30-50℃ for 1-1.5h to remove the solvent, then heat to 70-90℃ at a rate of 2 / min℃ and hold for 1.5-2h to promote siloxane crosslinking, and finally heat to 100-120℃ and hold for 1-1.5h to completely cure the shape memory polyurethane and epoxy resin, thus obtaining a corrosion-resistant rare earth alloy composite material.

[0075] Example 2

[0076] The corrosion-resistant rare earth alloy composite material, from the inside out or from the bottom up, includes a carbon steel substrate and a coating. The coating includes a rare earth alloy layer, a polydopamine-carbon nanotube hybrid layer, a CaSiO3-HAP composite mineralization layer, and a corrosion-resistant sealing layer.

[0077] The surface of the carbon steel substrate is etched with main pits at 15μm intervals. The main pits have a diameter of 50μm and a depth of 20μm. Then, at the bottom of the main pits of the carbon steel substrate, secondary pits with a diameter of 1μm and a depth of 1μm are etched at 1μm intervals.

[0078] The rare earth alloy layer is an Al-Zn-Ce-Mg-Sc alloy powder with a mass ratio of 50:30:10:7:3 and a particle size of 20-40μm. The surface of the rare earth alloy layer is a nitrided layer containing CeN and AlN with a thickness of 5-10nm.

[0079] Corrosion-resistant sealing layer includes:

[0080] A sol is formed by stirring 50% siloxane (KH560), 25% epoxy resin (E51), 20% shape memory polyurethane (Tg=60℃), 4.5% nano-montmorillonite, and 0.5% dibutyltin dilaurate.

[0081] A method for preparing corrosion-resistant rare earth alloy composite materials includes the following steps:

[0082] S100: Pretreatment of carbon steel matrix

[0083] S110: After ultrasonic rust removal in 5% dilute hydrochloric acid and cleaning with deionized water, the carbon steel substrate is etched with a femtosecond laser (pulse width 100 fs, wavelength 800 nm) to create main pits on the surface. The main pits mimic a honeycomb structure. Sub-pits are then etched at the bottom of the main pits. Finally, a second scan is performed to form 50-100 nm nanofibers (mimicking gecko foot bristles) on the surface of all pits. The laser energy density gradient is adjusted (5 J / cm² in the main pit area). 2 3J / cm in the secondary pit area 2 1J / cm nanofiber region 2 ), to avoid excessive heat damage;

[0084] S120: The carbon steel substrate treated with S110 is immersed in an ethanol-water mixed solution (volume ratio 1:1) containing 0.1 mol / L La2O3 quantum dots (particle size 5-10 nm) and treated at 60℃ and ultrasonic power 300W for 2 hours, allowing the quantum dots to adhere to the Fe on the carbon steel surface through electrostatic adsorption. 2+ La-Fe coordination bonds are formed; La2O3 quantum dots act as "molecular rivets" to provide atomic-level bonding sites for subsequent rare earth alloy layers, while rare earth elements are introduced in advance to reduce the subsequent diffusion energy barrier;

[0085] S200: Deposition and densification of rare earth alloy layers

[0086] S210: Place Al-Zn-Ce-Mg-Sc alloy powder in supercritical CO2 fluid (temperature 31℃, pressure 7.3MPa), add 0.5% CeCl3 as activator, stir for 1-1.5h to form activated powder with CeO2 nano-active layer on the powder surface, the thickness of CeO2 nano-active layer is 5-10nm;

[0087] S220: After the carbon steel matrix treated with S210 is subjected to gradient preheating, the temperature of the central region of the gradient preheating is 350℃ and the temperature of the edge region is 250℃. Supercritical He is used as the carrier gas (pressure 4MPa, temperature 150℃). The activation powder is sprayed onto the carbon steel matrix at a velocity of 800m / s, while a DC electric field (voltage 500V, current density 10mA / cm²) is applied. 2 The electric field promotes charge transfer on the surface of powder particles, thereby accelerating ion diffusion.

[0088] S230 places the deposited rare earth alloy layer in a 0.5T strong magnetic field and simultaneously applies a high-energy electrical pulse (voltage 1000V, pulse width 50μs, frequency 100Hz) and scans along the coating thickness direction for 5 minutes. The magnetic field causes the rare earth phase (such as CeZn5) in the coating to align in the direction of the magnetic field. The Joule heating and electroplastic effect of the electrical pulse causes the micropores and microcracks to close.

[0089] S240: Under a vacuum degree of 10 -3 In the reaction chamber of Pa, a N2-Ar mixed gas (volume ratio 1:3) is introduced, radio frequency plasma (power 300W) is applied, and nitriding is performed at 200℃ for 1.5-2h to form a 5-10μm nitrided layer containing CeN and AlN on the coating surface.

[0090] S250: Spray a mixture of dopamine solution (2 g / L concentration), 1.5% benzotriazole (0.3 g / L concentration), and 0.1% carbon nanotubes (50 nm diameter) with pH=8.5 onto the rare earth alloy layer treated in step S240, and dry it at 30°C for 6 h to form a polydopamine-carbon nanotube hybrid layer (1-2 μm thickness).

[0091] S260: Immerse the rare earth alloy layer treated in step S250 in an immersion solution containing 0.05 mol / L Ca. 2+ With 0.03 mol / L SiO3 2- In simulated body fluids, mineralization at 37℃ for 36-48 hours resulted in the formation of a CaSiO3-HAP composite mineralization layer.

[0092] S300: Forming of corrosion-resistant sealing layer

[0093] S310: Siloxane, epoxy resin, shape memory polyurethane, nano-montmorillonite, mixed and then dibutyltin dilaurate catalyst is added and stirred to form a sol.

[0094] S320: Vacuum dip coating (vacuum degree -0.09MPa) is used to penetrate the sol into the micropores of the rare earth alloy layer, ensuring a penetration depth of 3-7μm. After removal, it is allowed to level in the air for 0.5-1h.

[0095] S330: First, treat in a vacuum oven at 30-50℃ for 1-1.5h to remove the solvent, then heat to 70-90℃ at a rate of 2 / min℃ and hold for 1.5-2h to promote siloxane crosslinking, and finally heat to 100-120℃ and hold for 1-1.5h to completely cure the shape memory polyurethane and epoxy resin, thus obtaining a corrosion-resistant rare earth alloy composite material.

[0096] Example 3

[0097] The corrosion-resistant rare earth alloy composite material, from the inside out or from the bottom up, includes a carbon steel substrate and a coating. The coating includes a rare earth alloy layer, a polydopamine-carbon nanotube hybrid layer, a CaSiO3-HAP composite mineralization layer, and a corrosion-resistant sealing layer.

[0098] The surface of the carbon steel substrate is etched with main pits at 20μm intervals. The main pits have a diameter of 60μm and a depth of 25μm. Then, at the bottom of the main pits on the carbon steel substrate, secondary pits with a diameter of 2μm and a depth of 1μm are etched at 3μm intervals.

[0099] The rare earth alloy layer is an Al-Zn-Ce-Mg-Sc alloy powder with a mass ratio of 53:25:12:7:3 and a particle size of 20-40μm. The surface of the rare earth alloy layer is a nitrided layer containing CeN and AlN with a thickness of 5-10nm.

[0100] Corrosion-resistant sealing layer includes:

[0101] A sol is formed by stirring 50% siloxane (KH560), 25% epoxy resin (E51), 20% shape memory polyurethane (Tg=60℃), 4.5% nano-montmorillonite, and 0.5% dibutyltin dilaurate.

[0102] The preparation method of the corrosion-resistant rare earth alloy composite material is the same as in Example 2.

[0103] Comparative Example 1

[0104] The difference between this comparative example and Example 2 is that the carbon steel substrate surface was not etched with primary and secondary pits.

[0105] Comparative Example 2

[0106] The difference between this comparative example and Example 2 is that the carbon steel substrate surface was not scanned with nanofibers.

[0107] Comparative Example 3

[0108] The difference between this comparative example and Example 2 is that step S120 was not performed.

[0109] Comparative Example 4

[0110] The difference between this comparative example and Example 2 is that the rare earth alloy layer uses Al-Zn-Ce-Mg alloy powder, and the mass ratio of Al-Zn-Mg-Sc alloy powder is 60:30:7:3.

[0111] Comparative Example 5

[0112] The difference between this comparative example and Example 2 is that the rare earth alloy layer uses Al-Zn-Ce-Mg alloy powder, and the mass ratio of Al-Zn-Ce-Mg alloy powder is 50:30:10:10.

[0113] Comparative Example 6

[0114] The difference between this comparative example and Example 2 is that 0.5% CeCl3 was not added in step 210.

[0115] Comparative Example 7

[0116] The difference between this comparative example and Example 2 is that step S240 was not performed.

[0117] Comparative Example 8

[0118] The difference between this comparative example and Example 2 is that the anti-corrosion coating described in Example 3 of the patent with publication number CN106247028A, entitled "A Rare Earth Alloy Wear-Resistant Cast Pipe," is used instead of the corrosion-resistant sealing layer in this application. The specific preparation method is as follows:

[0119] S100: Pretreatment of carbon steel matrix

[0120] S110: After ultrasonic rust removal and deionized water cleaning in 5% dilute hydrochloric acid, the carbon steel substrate is etched with a femtosecond laser (pulse width 100fs, wavelength 800nm) to create main pits on the surface of the carbon steel substrate. The main pits mimic a honeycomb structure. Then, secondary pits are etched at the bottom of the main pits. Finally, a second scan is performed to form 50-100nm nanofibers (mimicking gecko foot bristles) on the surface of all pits. The laser energy density gradient is adjusted (5J / cm2 in the main pit area, 3J / cm2 in the secondary pit area, and 1J / cm2 in the nanofiber area) to avoid excessive thermal damage.

[0121] S120: The carbon steel substrate treated with S110 is immersed in an ethanol-water mixed solution (volume ratio 1:1) containing 0.1 mol / L La2O3 quantum dots (particle size 5-10 nm) and treated at 60℃ and ultrasonic power 300W for 2 hours. This allows the quantum dots to form La-Fe coordination bonds with Fe2+ on the carbon steel surface through electrostatic adsorption. The La2O3 quantum dots act as "molecular rivets," providing atomic-level bonding sites for the subsequent rare earth alloy layer. At the same time, the rare earth elements are pre-introduced to reduce the subsequent diffusion energy barrier.

[0122] S200: Deposition and densification of rare earth alloy layers

[0123] S210: Place Al-Zn-Ce-Mg-Sc alloy powder in supercritical CO2 fluid (temperature 31℃, pressure 7.3MPa), add 0.5% CeCl3 as activator, stir for 1-1.5h to form activated powder with CeO2 nano-active layer on the powder surface, the thickness of CeO2 nano-active layer is 5-10nm;

[0124] S220: After the carbon steel matrix treated with S210 is subjected to gradient preheating, the temperature of the central region of the gradient preheating is 350℃ and the temperature of the edge region is 250℃. Supercritical He is used as the carrier gas (pressure 4MPa, temperature 150℃). The activation powder is sprayed onto the carbon steel matrix at a velocity of 800m / s, while a DC electric field (voltage 500V, current density 10mA / cm²) is applied. 2 The electric field promotes charge transfer on the surface of powder particles, thereby accelerating ion diffusion.

[0125] S230 places the deposited rare earth alloy layer in a 0.5T strong magnetic field and simultaneously applies a high-energy electrical pulse (voltage 1000V, pulse width 50μs, frequency 100Hz) and scans along the coating thickness direction for 5 minutes. The magnetic field causes the rare earth phase (such as CeZn5) in the coating to align in the direction of the magnetic field. The Joule heating and electroplastic effect of the electrical pulse causes the micropores and microcracks to close.

[0126] S240: In a reaction chamber with a vacuum of 10⁻³ Pa, N₂-Ar mixed gas (volume ratio 1:3) is introduced, radio frequency plasma (power 300W) is applied, and nitriding is performed at 200℃ for 1.5-2 hours to form a 5-10 μm nitrided layer containing CeN and AlN on the coating surface.

[0127] S250: Spray a mixture of dopamine solution (2 g / L concentration), 1.5% benzotriazole (0.3 g / L concentration), and 0.1% carbon nanotubes (50 nm diameter) with pH=8.5 onto the rare earth alloy layer treated in step S240, and dry it at 30°C for 6 h to form a polydopamine-carbon nanotube hybrid layer (1-2 μm thickness).

[0128] S260: Immerse the rare earth alloy layer treated in step S250 in an immersion solution containing 0.05 mol / L Ca. 2+ With 0.03 mol / L SiO3 2- In simulated body fluids, mineralization at 37℃ for 36-48 hours resulted in the formation of a CaSiO3-HAP composite mineralization layer.

[0129] S300: Preparation and Spraying of Anti-corrosion Coating

[0130] S310: Select raw materials according to the chemical composition of the anti-corrosion coating, put each raw material into a grinding machine and grind for 4 hours, then stir evenly to obtain the anti-corrosion coating. The anti-corrosion coating has the following chemical components in parts by weight: 40 parts of organosilicon resin; 20 parts of epoxy resin; 12 parts of polytetrafluoroethylene propylene; 18 parts of toluene; 0.12 parts of sodium molybdate; 0.08 parts of disodium hydrogen phosphate; 1.4 parts of fatty acid polyethylene glycol ester; and 1 part of emulsified silicone oil.

[0131] S320: Apply the anti-corrosion coating to the coating treated in step S260, with a coating thickness of 0.4 mm.

[0132] Comparative Example 9

[0133] The difference between this comparative example and Example 2 is that the anti-corrosion coating described in Example 1 of the patent with publication number CN102418831A, entitled "A Multi-Alloy Composite Anti-corrosion Coating for Metal Pipes and Fittings," is used instead of the corrosion-resistant sealing layer in this application. The specific preparation method is as follows:

[0134] S100: Pretreatment of carbon steel matrix

[0135] S110: After ultrasonic rust removal and deionized water cleaning in 5% dilute hydrochloric acid, the carbon steel substrate is etched with a femtosecond laser (pulse width 100fs, wavelength 800nm) to create main pits on the surface of the carbon steel substrate. The main pits mimic a honeycomb structure. Then, secondary pits are etched at the bottom of the main pits. Finally, a second scan is performed to form 50-100nm nanofibers (mimicking gecko foot bristles) on the surface of all pits. The laser energy density gradient is adjusted (5J / cm2 in the main pit area, 3J / cm2 in the secondary pit area, and 1J / cm2 in the nanofiber area) to avoid excessive thermal damage.

[0136] S120: The carbon steel substrate treated with S110 is immersed in an ethanol-water mixed solution (volume ratio 1:1) containing 0.1 mol / L La2O3 quantum dots (particle size 5-10 nm) and treated at 60℃ and ultrasonic power 300W for 2 hours, allowing the quantum dots to adhere to the Fe on the carbon steel surface through electrostatic adsorption. 2+ La-Fe coordination bonds are formed; La2O3 quantum dots act as "molecular rivets" to provide atomic-level bonding sites for subsequent rare earth alloy layers, while rare earth elements are introduced in advance to reduce the subsequent diffusion energy barrier;

[0137] S200: Arc-sprayed alloy coating

[0138] S210: A multi-element alloy wire with a weight composition of Zn 56%, Al 41%, Mg 2.0%, and RE 1.0% (φ2.0mm) is used as the metal wire for arc thermal spraying, at a weight of 130g / m. 2 It is sprayed onto the surface of the pipe to form a multi-alloy composite anti-corrosion coating;

[0139] S300: Apply sealing finish coating

[0140] S310: Epoxy resin is coated on the surface of the multi-element alloy layer to seal the pores of the alloy layer. The thickness of the sealing finishing layer is 110μm.

[0141] Test items and test methods

[0142] Combined strength test

[0143] Tests were conducted according to GB / T5210-2006. Epoxy adhesive was used to bond the specimens of Examples 1-3 and Comparative Examples 1-9 to the test column. A tensile testing machine was used to apply a load at a rate of 5 mm / min, and the maximum tensile force at which the coating peeled off was recorded. The bond strength was then calculated.

[0144] Neutral salt spray corrosion test

[0145] The test was conducted according to GB / T10125-2021. The sample was placed in a salt spray chamber and continuously sprayed with 5% NaCl solution (pH=6.9) at a spray pressure of 98 kPa and a temperature of 35℃. After 2500 hours of testing, the corrosion area and weight loss rate were observed.

[0146] Acidic flue gas corrosion simulation test

[0147] The test was conducted according to GB / T19292.3-2018, using a corrosion test chamber, through which a mixed gas containing 0.1% SO2, 0.05% NO2, 5% O2, and 10% H2O (simulating flue gas composition) was introduced at a temperature of 150℃ and a pressure of 0.1 MPa for 1000 hours.

[0148] Regularly inspect the coating surface for corrosion products (use XRD analysis to determine if corrosion products such as Fe2O3 are generated) and calculate the corrosion rate.

[0149] Electrochemical performance testing

[0150] The test was conducted according to GB / T24196-2009, using a three-electrode system (the specimen as the working electrode and a saturated calomel electrode as the reference electrode), and the open circuit potential (OCP) was tested in a 3.5% NaCl solution for 30 consecutive days.

[0151] Abrasion resistance test

[0152] The test was conducted according to GB / T12444-2006. Quartz sand (particle size 50-100μm) was sprayed onto the coating surface at a speed of 20m / s (angle 30°) using compressed air. The weight loss was measured after 30 minutes of testing.

[0153] High-temperature antioxidant test

[0154] The test was conducted according to GB / T13303-1991. The sample was placed in a muffle furnace and kept at 400℃ in static air for 1000 hours. After cooling, the weight gain of the oxide scale was measured.

[0155] Self-repair performance test

[0156] A 50 μm microcrack was artificially created on the coating surface and placed in an acidic solution with pH=5 (simulating a corrosive environment). The impedance value was monitored for 100 h by electrochemical impedance spectroscopy (EIS) and the change in impedance value was observed (an increase in impedance indicates that the corrosion inhibitor is effective).

[0157] The specimen with cracks was heated to 60℃ (shape memory polyurethane Tg) and held for 1 hour. The cracks were then observed under a microscope to see if they had closed.

[0158] Test Results

[0159] The test results of Examples 1-3 and Comparative Examples 1-9 are shown in Tables 1 and 2.

[0160] Table 1

[0161]

[0162] Table 2

[0163]

[0164] Based on the above test results, we can conclude that:

[0165] Regarding bonding strength, Examples 2 and 3, due to the dual interfacial reinforcement (molecular bonding + chemical affinity) of the "polydopamine-carbon nanotube hybrid layer + CaSiO3-HAP mineralization layer," exhibit significantly higher bonding strength than Example 1 (without the polydopamine-carbon nanotube hybrid layer and CaSiO3-HAP composite mineralization layer). Comparative Examples 1 (without pits), 2 (without nanofibers), and 3 (without quantum dot pre-infiltration) lack a key element in the "tertiary interfacial bonding," resulting in a 30%-40% decrease in bonding strength. In Comparative Example 4 (without Ce), Ce strengthens the metallurgical bonding of the "matrix-rare earth alloy layer" through La-Fe-Ce coordination bonds in the quantum dot pre-infiltration stage and interfacial diffusion in the deposition stage. Without Ce, the interface relies solely on the physical interlocking of Al-Zn and Fe, leading to a decrease in bonding strength.

[0166] Regarding corrosion resistance, the acidic flue gas corrosion rates (0.0005-0.0006 mm / a) of Examples 2 and 3 were significantly lower than those of the comparative example. This is attributed to the synergistic effect of "rare earth sacrificial anode (Sc stable potential) + pH-responsive corrosion inhibition release + self-healing sealing agent". In Comparative Example 4 (without Ce), the absence of Ce led to a decrease in the density of the rare earth alloy layer (preventing the formation of a CeO2 nano-active layer to fill the pores), making it easier for the corrosive medium to penetrate the matrix. Ce is the core regulating element for the activity of the sacrificial anode, forming (Al,Ce)Fe2 intermetallic compounds with Al and Zn. Without Ce, the alloy electrode... The potential is mainly dominated by Al-Zn, with a positive shift and a significant decrease in stability. In Comparative Example 5 (without Sc), the absence of Sc coarsens the rare earth alloy grains, increases grain boundary defects, and becomes a channel for the penetration of corrosive media, resulting in a decrease in the anti-corrosion effect. The 4d electron layer structure of Sc can form stable intermetallic compounds with Al and Zn, anchoring free electrons through the "electron trap" effect. After the absence of Sc, the electrode potential is mainly dominated by the solid solution of Al-Zn, and the randomness of electron transitions increases, leading to a larger amplitude of potential fluctuations. In Comparative Example 7 (without nitride layer), due to the absence of the "active reserve layer", the corrosion rate increases by 3 times compared to Example 2.

[0167] Regarding wear resistance and high-temperature performance, the wear weight loss and oxidation weight gain in Examples 2 and 3 were significantly lower than those in the comparative example. The principle is that the synergistic effect of the magnetic and electric dual fields (0.5T magnetic field + 1000V electric pulse) promotes the bonding of Ce, Al and N, forming a composite nitrided layer of CeN (hardness 450HV) and AlN (hardness 380HV), which increases the hardness by 40% compared to the traditional nitrided layer and enhances the resistance to fly ash wear. The nano-montmorillonite lamellae in the sealing agent are arranged parallel to the surface, forming a "maze effect" that allows fly ash particles to be washed away. The path lengthening reduces wear weight loss, and gradient curing enables siloxane to form a highly cross-linked Si-O-Si network, which remains structurally stable even at 400℃, thus reducing oxidation weight gain. The wear weight loss of Comparative Example 7 (without nitride layer) is twice that of Example 2. Due to the lack of nitride layer protection, the surface hardness of the rare earth alloy layer decreases, making it unable to resist the cutting and wear of fly ash particles. The oxidation weight gain of Comparative Examples 1-3 (with many interface defects) is relatively high because the porosity of the coating is relatively large, allowing oxygen to easily penetrate into the substrate through the pores and trigger an oxidation reaction.

[0168] Regarding self-healing performance, the EIS impedance change rate and crack closure rate of Examples 2 and 3 were significantly higher than those of the comparative example. The key factor was that when pH < 6 in the initial stage of corrosion, the amine matrix protonation of the PDA / CNTs layer generated electrostatic repulsion, causing benzotriazole to be rapidly released from the CNTs surface, forming an adsorption film on the metal surface. The EIS impedance value increased with the thickness of the film. In the sealing agent, the shape memory polyurethane (SMPU) at Tg = 60℃ restored the original conformation of its soft segments, resulting in a crack closure rate of over 90% within 1 hour for cracks within 50 μm, preventing further penetration of the corrosive medium. (Comparative example) 1-3 did not employ the "quantum dot infiltration + multi-level texture" interface strengthening method, resulting in high coating porosity and insufficient adhesion between the PDA / CNTs hybrid layer and the substrate. This led to rapid penetration of corrosive media, with local crack propagation exceeding the repair threshold of shape memory polyurethane (SMPU), resulting in low crack closure rates. CNTs agglomerated due to weak interfacial adhesion, reducing benzotriazole pre-adsorption by 60%. Even at pH < 6, the release amount was only 30% of that in the example, failing to form an effective protective film and resulting in low EIS impedance. Comparative Example 4 (without Ce) showed a decrease in rare earth alloy layer density, leading to... - The penetration rate was three times that of the example, and local pitting corrosion could form a 100μm deep corrosion pit within 24 hours. In contrast, the crack closure of SMPU required 1 hour, and the formation of the protective film released by the corrosion inhibitor required 30 minutes. There was a significant time difference between corrosion and repair, and the final crack closure rate was only 61.22%. Comparative Example 5 (without Sc): The electrode potential fluctuated by ±0.06V, and the sacrificial anode protection showed "intermittent failure". This resulted in an excessively fast corrosion rate, which caused the EIS impedance value to rise slowly due to the destruction of the film layer. The change rate of the EIS impedance value was only 22.61%. The crack closure rates of Comparative Examples 8 and 9 were low because the sealing agent used ordinary epoxy resin, which has no shape memory function. Once the crack was formed, it continued to expand, eventually leading to coating failure.

[0169] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A corrosion resistant rare earth alloy composite material, characterized by, From inside to outside, or from bottom to top, sequentially include carbon steel substrate and coating, the coating includes rare earth alloy layer and corrosion-resistant sealing layer; The surface of the carbon steel substrate is etched with main pits at an interval of 10-20 μm, the diameter of the main pits is 40-60 μm, and the depth is 15-25 μm, the surface of the carbon steel substrate is etched with secondary pits at an interval of 1-3 μm, the diameter of the secondary pits is 1-2 μm, and the depth is 0.5-1 μm, the surface of the main pits and the secondary pits of the carbon steel substrate has nanofiber of 50-100 nm, after pretreatment, the surface of the carbon steel substrate is immersed in an ethanol-water mixed solution containing La2O3 quantum dots to form La-Fe coordination bond; The rare earth alloy layer is Al-Zn-Ce-Mg-Sc alloy powder, and the surface of the rare earth alloy layer is a nitrided layer containing CeN and AlN; The corrosion-resistant sealing layer includes: Siloxane 40-60%, epoxy resin 25-35%, shape memory polyurethane 10-20%, nano-montmorillonite 3-8%, dibutyltin dilaurate 0.3-0.8%, and the stirring forms a sol.

2. The corrosion resistant rare earth alloy composite of claim 1, wherein, The mass ratio of the Al-Zn-Ce-Mg-Sc alloy powder of the rare earth alloy layer is (45-55):(25-35):(8-12):(5-10):(1-3), and the particle size is 20-40 μm.

3. The corrosion resistant rare earth alloy composite of claim 1, wherein, The coating further includes a polydopamine-carbon nanotube hybrid layer and a CaSiO3-HAP composite mineralization layer; The polydopamine-carbon nanotube hybrid layer is arranged between the corrosion-resistant sealing layer and the rare earth alloy layer, and the CaSiO3-HAP composite mineralization layer is arranged between the polydopamine-carbon nanotube hybrid layer and the corrosion-resistant sealing layer.

4. A method for producing the corrosion resistant rare earth alloy composite material according to any one of claims 1 to 3, characterized by, The method includes the following steps: S100: Pretreatment of carbon steel substrate S110: After ultrasonic rust removal and cleaning of the carbon steel substrate in dilute hydrochloric acid, the carbon steel substrate is subjected to interval etching of main pits and secondary pits by laser, and nanofiber is formed on the surface of all pits by secondary scanning S120: immersing the carbon steel substrate treated in S110 into an ethanol-water mixed solution containing La2O3 quantum dots, and after ultrasonic treatment, the quantum dots are electrostatically adsorbed on the surface Fe of the carbon steel through the formation of La-Fe coordination bonds 2+ to form La-Fe coordination bonds; S200: Deposition and densification of rare earth alloy layer S210: The Al-Zn-Ce-Mg-Sc alloy powder is placed in supercritical CO2 fluid, CeCl3 is added as an activator, and the powder surface is activated to form an active layer with CeO2 nanoactivity after stirring for 1-1.5 h; S220: After gradient preheating of the carbon steel substrate treated in S210, the activated powder is sprayed onto the carbon steel substrate with supercritical He as carrier gas, and a direct current field is applied to promote surface charge transfer of powder particles and accelerate ion diffusion; S230: The deposited rare earth alloy layer is placed in a strong magnetic field, and a high-energy electric pulse is applied to scan along the thickness direction of the coating; S240: In a vacuum reaction chamber, N2-Ar mixed gas is introduced to apply radio frequency plasma, and the coating surface is nitrided at 200℃ for 1.5-2 h to form a nitrided layer containing CeN and AlN; S300: Forming of corrosion-resistant sealing layer S310: Siloxane, epoxy resin, shape memory polyurethane, nano-montmorillonite, after mixing, dibutyltin dilaurate catalyst is added, and the stirring forms a sol. S320: the sol is infiltrated into the rare earth alloy layer by vacuum dip coating, ensuring that the penetration depth reaches 3-7 μm, and after taking out, leveling in the air for 0.5-1 h; S330: first, the temperature is raised to 30-50℃ in a vacuum oven for 1-1.5 h to remove the solvent, then the temperature is raised to 70-90℃ for 1.5-2 h to promote the crosslinking of siloxane, and finally the temperature is raised to 100-120℃ for 1-1.5 h to completely cure the shape memory polyurethane and epoxy resin.

5. The method of claim 4, wherein the method further comprises the step of: In step S220, the temperature center region of the gradient preheating of the carbon steel substrate is 300-400℃, and the edge region is 200-300℃.

6. The method of claim 4, wherein the method further comprises the step of: Before the sol is infiltrated into the rare earth alloy layer in step S320, it also includes: S250: spraying a dopamine solution and a carbon nanotube mixed solution on the rare earth alloy layer treated in step S240 to form a polydopamine-carbon nanotube hybrid layer; S260: immersing the rare earth alloy layer treated in step S250 into a Ca 2+ with SiO3 2- and HAP in a simulated body fluid at 37℃ for 36-48h to form a CaSiO3-HAP composite mineralized layer.

7. The method of claim 6, wherein the method further comprises the step of: In step S250, the pH of the dopamine solution is 8-9, benzotriazole is added to the dopamine solution, and the addition amount of the carbon nanotube is 0.07-0.12% of the dopamine solution; ​ In step S260, Ca 2+ has a concentration of 0.05 mol / L, and SiO3 2- has a concentration of 0.03 mol / L.

8. Use of the corrosion resistant rare earth alloy composite material according to any one of claims 1 to 3, characterized in that Tube bundle for use in an air preheater.

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